The invention relates to a method for the manufacture of brushware having plastic bristles, which are continuously extruded as monofilaments, cut to the desired length and fixed individually or in groups as a bristle facing to a bristle carrier. The invention also relates to the brushware manufactured according to the method.
Brushware, such as tooth, massage, paint, textile and carpet brushes, but also numerous technical and industrial brushes, only fulfil their use function over a specific period of time, which is almost exclusively determined by wear to the bristles and is otherwise dependent on the nature of the brushware and the desired working result.
For example, brushes used in the personal hygiene sector have a relatively short use period and include massage, cosmetic and in particular toothbrushes. Therefore the fundamental problem of the invention will be illustrated in exemplified manner relative to toothbrushes.
Even in the last century it was recognized in connection with toothbrushes (U.S. Pat. No. 74,560 of 1868), that bristles which, at the time were exclusively made from animal hair, have sharp edges or seams as a result of cutting processes and which can lead to injuries to the gingiva. In order to remove such edges and seams, toothbrush bristles, but also bristles for other brushes used on the human body, are rounded at the use-side ends by mechanical abrasion. U.S. Pat. No. 74,560 proposes a conical abrading or grinding with a rounded tip.
In recent times toothbrushes have almost exclusively had plastic bristles, which are cut to the desired length from extruded monofilaments. The short cuts obtained in this way are generally combined into bundles, which are then fixed to the toothbrush head. It is still necessary to round the use-side ends, which still mainly takes place by grinding or abrading. In the final state, the bristle has an identical, cylindrical cross-section over its length and is rounded to a dome-shaped tip at its use-side end. Of late, conical abraded bristles are used, so that at least individual bristles of the bristle facing better penetrate the interdental spaces and can also effectively clean fissures on the tooth surface. However, the bristle must still have a rounded tip, in order to prevent injuries to the gingiva or also, as recent scientific investigations have revealed, brush lesions to the tooth. This more particularly applies in the case of sensitive gingiva or dental necks, which exist in almost 50% of users.
For the aforementioned reasons, bristles are already used in toothbrushes which are extruded from plastics monofilaments, but which are split to so-called flags at their use-side ends. In the lower, unsplit region of the bristle, use is made of the desired bristle bending capacity, whereas the flags permit a careful cleaning of the tooth surfaces and inter-dental spaces, as well as a careful massaging action for the gingiva. Similar combinatorial effects are obtained with brushes, which comprise a core and a sleeve or shell, which are generally made from different plastics by co-extrusion. The core mainly meets the strength requirements, whereas the sleeve is responsible for the cleaning and hygienic function.
When a toothbrush is in regular use relatively rapidly bristle wear arises and as a result the bristles lose their aforementioned characteristics. Wear more particularly starts on the bristle jacket, so that cylindrical bristles are tapered towards the bristle end and bristles with a conical end are pointed after a certain period of use. In both cases the round tip is worn away, usually in an irregular manner, so that the effects sought by the rounding are lost. In the case of bristles comprising a core and a sleeve, initially the sleeve is worn away in the vicinity of the bristle end and the core is exposed. In the case of bristles with flags, the wear progresses even faster due to the thin cross-sections of the flags. Since this leads to a constant decrease in the free length of the flags, conversely there is an undesired increase to their rigidity and there is a risk of the solid bristle stump causing injury.
For the aforementioned reasons dentists recommend the replacement of toothbrushes after a few weeks. The user frequently fails to do this, because it is impossible to optically perceive wear as a result of the limited bristle cross-sections, which are between 0.15 and 0.225 mm and even after a long period of use the toothbrush gives the optical appearance of still being usable.
Numerous attempts have been made to render visible to the user the degree of wear of a toothbrush. Thus, it is known (EP 366 100) to construct part of the toothbrush handle from a material which discolors or even dissolves as a result of use, so that in the first case it is rendered optically visible to the user and in the second through the non-usability of the handle that the toothbrush must be replaced. However, understandably, such a design is completely practically inappropriate.
According to another known proposal the bristle is made from a core and a jacket with a different color. As a result of the abrading action occurring on brushing, in the vicinity of the use-side ends the jacket is worn away and consequently the differently colored core material becomes visible, so that the user is made optically aware of the need to replace the toothbrush (DE 34 00 941, U.S. Pat. No. 4,802,255, 5,313,909, 5,268 005, WO94/10 539). Bristles of this type have already entered practical use, because no other appropriate solutions exist. However, the amount of wear is not apparent in a not with sufficiently high contrast manner to lead the user to replace the toothbrush at the correct time. The reproducibility of such a use indication is also inadequate. Frequently such an optical indication, only rendered visible by wear to the bristle, is only noticed at a late time or not at all. This method also presupposes a two-part bristle construction of core and sleeve.
This method fails in the case of modern bristle shapes, e.g. with a conical tapering bristle end, because either the jacket and therefore the entire bristle must have an excessive cross-section, or the core must be differently colored over its length, which is not technically possible by extrusion. This method also fails with bristles having flags or with brushes in which the use-side ends of the bristles are in a non-planar envelope or envelope surface.
The problem of the present invention is to continuously provide the brushware user with optical information concerning the existing use state and the degree of wear independently of the actual abrasion situation when using the brushware.
According to the invention, this problem is solved in that the monofilament after extrusion or the bristles produced therefrom is provided with at least one substantially linear boundary detectable on the bristle facing of the finished brushware as a color-contrasted marking, at a distance from the use-side end of the bristles representing the use state.
Thus, with the method according to the invention, the marking indicating the degree of use or the need to replace the brush is applied subsequently, namely after extrusion, to the monofilament or the cut-to-size bristle, in the form of a color-contrasted, linear boundary, which has a distance from the use-side end of the bristle representing the use state and therefore the degree of wear. This distance, i.e. the position of the boundary, can be fixed according to substantially objective criteria, in that the finished brushware undergoes a long-term or endurance test and the nature and extent of the wear is macroscopically investigated on the individual bristles. On the basis of the average values of the bristle wear of the entire bristle facing obtained in this way, it is possible to establish the particular bristle length, in which disadvantageous wear or abrasion phenomena for the correct function of the brush appear. Correspondingly the boundary is then applied to the monofilament or bristle.
With the method according to the invention it is possible to provide with a use indication bristles having random shaping such as single-element monofilaments, multiple-element monofilaments, co-extruded monofilaments, bristles with flags or conical tapering bristle ends, which is clearly perceptible to the user and is not dependent on the abrasion situation. On the finished brushware, it is only necessary to provide individual bristles or individual bristles within several bundles with the color-contrasted marking, in order to indicate the degree of wear. These bristles or bundles will in particular be provided in the brush areas where, on the basis of the endurance tests, wear progresses fastest. Use will only be made for the application of the boundary of those bristles which are on the outside in the bristle facing, which offers the advantage that the marking or boundary can also be subsequently applied to the finished brush.
It is also possible to provide several color-contrasted, substantially parallel, linear boundaries at different distances from the use-side end of the bristles, so as to represent different use states for different stages of wear.
This method is particularly suitable for brushware, where micro-range wear does not lead to the bristles becoming unusable and more particularly for brushware where the functional quality merely decreases with increasing shortening of the bristles, e.g. the bristles become stiffer through shortening and consequently the brush becomes harder, or the absorption of the bristle facing for the application media decreases due to the shorter capillaries between the bristles. For such brushware it is largely up to the user to decide the time or wear state when the brush no longer satisfies his individual requirements.
The linear boundaries can be formed by the boundary lines of strip-like markings and it is possible to apply several strip-like markings of different width for indicating different use states.
As has already been indicated, the boundary on the monofilament can be produced after extrusion, e.g. in intervals or distances following the subsequent bristle length. However, the boundary can also be applied to the finished bristle after cutting to size, but preferably the boundary is produced on the outer bristles of the bristle facing before of after the fixing thereof to the bristle carrier. In the first-mentioned case, the bristle facing is fixed in a holder in the final configuration of the bristles or bundles (e.g. EP 346 646) and transferred with the holder to the brush manufacturing machine. It is preferably an injection mould, in which the bristle carrier plastics material is molded round the bristle facing at the fixing-side ends of the bristles. In this variant of the method, as for the marking of the bristles on the finished brushware, the boundary can be applied very simply and very precisely on the basis of the results obtained in the endurance tests. It can also be locally precisely defined should this prove necessary and as a result of the close juxtaposition of the bristles there is generally no need for each outer bristle to carry a marking, because the marking applied to several bristles over the entire extension of the bristle facing is optically visible as a linear or strip-like boundary. This more particularly applies for boundaries, which are produced in the form of dots or strips or as part of a circumferential line on the bristles.
Finally, this method variant has the advantage that different technical methods can be utilized for applying the marking and further reference will be made thereto hereinafter.
In the case of toothbrushes the bristle facing is frequently contoured, in order to adapt the brush face to the contours of the denture, teeth or mouth. Therefore the use-side ends of the bristles are in an envelope diverging from the plane. For such brushes, particularly toothbrushes, according to the invention the boundary is applied in a preferably parallel position corresponding to said envelope.
Thus, it is ensured that even for brushes having an irregular contour, the use state of the brush or the degree of wear of the bristles can be seen at all times in all areas of the bristle facing. For brushes of this type, the bristles or bundles need only be finished in the manner according to the invention in those areas where the greatest wear is observed.
The boundary can also be produced by the boundary line of differently colored zones in the longitudinal direction of the bristles, which can be obtained by subsequent treatment using physical processes.
For bristles comprising a core and a sleeve, e.g. produced by co-extrusion, the boundary can be produced on the core, sleeve or both, in order to indicate different use states or degrees of wear. For example, the core can be provided with a boundary having a smaller distance from the use-side end than a marking applied to the sleeve. In the case of jacket material removal caused by use, initially the marking applied to the core is exposed, in order to e.g. indicate to the user that wear has reached a significant level, whereas the marking made on the sleeve indicates to the user that the brush should be replaced. This construction is particularly recommended for those brushes, whose sleeve contains fillers, e.g. those having an abrasive action.
The sleeve can be made from a transparent plastic and the core can be provided with a translucent boundary. During brush use, the boundary is constantly perceptible with a specific color intensity. If during use the jacket is removed, the boundary finally appears with a possibly more intense color, in order to bring about a brush replacement on the part of the user.
According to a preferred development, the monofilament used for producing the bristles is extruded from a pigment-filled plastic, which reacts to laser beams with a color change, the boundary being produced by the action of laser beams on the monofilament or the bristles produced therefrom.
Laser technology is particularly suitable in the method according to the invention, because the marking is not only produced on the surface, but also in the depth of the monofilament or bristles. The marking can also be precisely defined and localized by the parallel-beam laser light. It is also possible to influence the depth of the marking by the laser parameters. In the case of two or multiple-element bristles, it is also possible to use a pigmented monofilament for a single element, so that only the latter is marked. For a monofilament comprising a core and a sleeve, only the core or only the sleeve need be filled with pigments, in order to apply the marking either to the sleeve or to the core. If both are filled with pigments, markings can be applied to the sleeve and the core for indicating different use states.
It is also possible to extrude the monofilament from two polymers with different laser beam absorption coefficients. In this case a pigmentation is unnecessary and marking mainly takes place by color change at the interface to the more strongly absorbing polymer. If both polymers are co-extruded to a monofilament, the color change need only take place at the interface of core and sleeve.
Laser technology offers the particular advantage that the uneven lateral face of the bristle facing formed from a plurality of juxtaposed, standing bristles and which is therefore in the form of an irregularly corrugated envelope of the outer bristle jackets can still be provided with an optically closed-appearing marking. Laser technology also offers the possibility of applying an explanatory inscription below and in the same way as the boundary rendering the user state legible to the user.
The ink jet process can be used in place of laser technology for applying the boundary and in it the ink applied penetrates the micro-pores of the bristle surface. Other processes with a similarly precise dye or color application can be used.
Instead of this, the monofilament can be extruded with a thin, chromophoric top coat and the boundary is produced by the removal of the top coat. This removal can once again take place by laser beams.
The invention also relates to the brushware manufactured according to the aforementioned methods, which are characterized in that at least part of the outer bristles in the bristle facing have a color-contrasted, substantially linear boundary in a distance from the use-side end of the bristle representing the use state.
Embodiments of such brushware are characterized in claims 22 to 36.